Pcdhβ deficiency affects hippocampal CA1 ensemble activity and contextual fear discrimination

Abstract

Clustered protocadherins (Pcdhs), a large group of adhesion molecules, are important for axonal projections and dendritic spread, but little is known about how they influence neuronal activity. The Pcdhβ cluster is strongly expressed in the hippocampus, and in vivo Ca²⁺ imaging in Pcdhβ-deficient mice revealed altered activity of neuronal ensembles but not of individual cells in this region in freely moving animals. Specifically, Pcdhβ deficiency increased the number of large-size neuronal ensembles and the proportion of cells shared between ensembles. Furthermore, Pcdhβ-deficient mice exhibited reduced repetitive neuronal population activity during exploration of a novel context and were less able to discriminate contexts in a contextual fear conditioning paradigm. These results suggest that one function of Pcdhβs is to modulate neural ensemble activity in the hippocampus to promote context discrimination.

Keywords: CA1; Ca2+ imaging; Clustered protocadherin; Contextual fear memory; Discrimination; Ensemble; Hippocampus; Pcdhβ.

Fig. 1

Pcdhβ deficiency reduces repetitive neuronal activity in the hippocampus. a Pcdhβ deletion. b Induction of CaMKII-G-CaMP7 by AAV and implantation of GRIN lens over the right hippocampal CA1 region. c Ca²⁺ imaging in home cage (pre) and square context (sq). d Schematic of the correlation matrix analysis. Representative images of correlation matrices for activation in Wt (e) and Δβ (f) mice. g Summation of correlation coefficients between sessions (n = 5 Wt mice, 4 Δβ mice). Data are means ± standard errors of the means (SEMs). **P < 0.01 (adjusted P-value from Bonferroni’s multiple-comparison test)

Fig. 2

Pcdhβ deficiency affects ensemble size and the proportion of neurons shared between ensembles. Representative images of binarized basis matrices from Wt (a) and Δβ (b) mice. Yellow dots represent the cells contributing to the ensemble. c–d Normalized number of ensembles according to ensemble size. Statistical values from Bonferroni’s multiple-comparison test are provided in Additional file 6: Table S1 (n = 5 Wt mice, 4 Δβ mice). Data are means ± SEMs. **P < 0.01 (adjusted P-value from Bonferroni’s multiple-comparison test). Percentages of neuronal cells contributing to one ensemble (open bars) and multiple ensembles (pattern and solid bars) in Wt and Δβ mice during pre (e) and sq (f) sessions. ****P < 0.0001 (chi-square test)

Fig. 3

Pcdhβ deficiency impairs context discrimination. a Schematic image of contextual fear conditioning task. b Freezing levels in test sessions. Square: F_{(21, 18)} = 2.140, P = 0.1080; t₃₉ = 1.141, P = 0. 2607; circle: F_{(18, 21)} = 1.153, P = 0.7479; t₃₉ = 1.301, P = 0.2008; unpaired t-test. c Discrimination indices of both contexts. F_{(18, 21)} = 1.645, P = 0.2737; t₃₉ = 2.310, P = 0.0263; unpaired t-test. (n = 19 Wt mice, 22 Δβ mice). Data are means ± SEMs